1. Field of the invention
The present invention relates to an instrument for separating liquid from solid material in solid material-containing liquid samples and a process utilizing the instrument. This instrument is designed to be advantageously employable in combination with a dry analytical element.
2. Description of prior art
There are already known a number of analytical systems for detecting and quantitatively determining biochemically active analytes in a liquid sample by using a dry analytical element in the layer or sheet form. For example, U.S. Pat. No. 3,050,373 is mentioned. According to these analytical systems, a component to be analyzed (i.e., analyte) contained in the liquid sample and a reactive compound responsive physically or chemically to the analyte are brought into contact with each other to perform a reaction. An amount of the reaction product or the unreacted substance is then determined by photometry, fluorometry, or a method using a radioactive isotope, to quantitatively determine the analyte.
In the use of whole blood as the liquid sample, the trouble resides in that dense-colored solid materials such as red blood cells disturb the photometric determination. In heretofore known procedures, it has been proposed that a blood cell filtration layer be specifically provided to trap the red blood cells therein. A representative blood cell filtration layer is described in Japanese Patent Publication No. 53(1978)-21677 and is composed of a porous material having an appropriate porosity to filter off the blood cells and the like on the surface of the layer. Accordingly, it is suggested that the pore size of the filtration layer is set to be in the range of 1 to 5 .mu.m which is smaller than the blood cell size (i.e., 7-30 .mu.m). Under these conditions, the blood cells and the like do not permeate the filtration layer and are left on the surface of the layer. This filtration is named "surface filtration". Thus, the liquid portion such as serum or plasma is separated from blood cells and the like. The analytical procedure using an analytical element provided with the filtration layer such as above is advantageous as compared with the conventional procedure involving centrifugal pretreatment of whole blood. However, the filtration rate is not high, and further, plugging sometimes occurs.
Japanese Patent Provisional Publication No. 57(1982)-53661 discloses an instrument for recovering serum or plasma by removing solid material from blood on a layer which is composed of specific glass fibers having a density of 0.1 to 0.5 g/cm.sup.3 and a mean diameter of 0.2 to 0.5 .mu.m. It is not said that this separation instrument shows satisfactory blood cell-separation ability. For instance, the working example in the publication shows a practical separation of serum (or plasma) from blood cells by setting the amount of serum or plasma to not more than 50% of the whole absorbing capacity of the layer and further by providing a hydrophobic barrier layer.